The function of calmodulin and of the major 51,000 Mr protein in cerebral cortex postsynaptic densities (PSD), and the physiological significance of these funtions, will be examined in two ways. First, antibodies to these two proteins will be injected into neuronal cells by micromanipulation, and the effects of these will be monitored electrophysiologically, under normal conditions and under depolarization conditions. Second, a spin-label will be attached to calmodulin, and the spin-labeled calmodulin reconstituted into PSDs of a synaptosome preparation depleted of calmodulin. The synaptosome preparation will be depolarized in various ways, and the ESR signals recorded to observe any change in the movement of the calmodulin during the post-synaptic response. In another project, an attempt will be made to purify alpha-latrotoxin from American black widow spiders, since the biochemical procedures used for the Italian spiders were unsuccessful. This attempt will be based on the strong specific binding of the toxin to synaptic membranes and the removal of the toxin from the membranes by antibodies to it.